CFD-DEM study on transport and retention behaviors of nZVI-clay colloids in porous media

Transportation process of nano scale zero valent iron (nZVI) in clay-rich soils is complicated and crucial for in-situ remediation of contaminated sites. A coupled computational fluid dynamic and discrete element method (CFD-DEM) was used to investigate the interplays of repulsive and attractive forces and the injection velocity of this process. The screened Coulomb's law was used to represent the electrostatic interaction, and surface energy density was introduced to represent the effects of the van der Waals interaction. A phase diagram was constructed to describe the interplay between injection velocity and repulsive force (in terms of charge of colloids). Under the boundary and initial conditions in this study, clogging formed at low repulsive force (colloidal charge = -1 ×10-15 C), where increment of injection velocity (from 0.002 m/s to 0.02 m/s) cannot prevent clogging, as in the case of bare nZVI transportation with limited mobility; On the other hand, excessive repulsive force (charge = -4 ×10-14 C) is detrimental to nZVI-clay transportation due to repulsion from the concentrated colloids in pore throats, a phenomenon as in the overuse of stabilizers and was defined as the "membrane repulsion effect" in this study. At moderate charge (-1 ×10-14 C), injection velocity increment induced clogging due to aggregates formed at the windward of cylinder and accumulated at the pore throats.

Vertical flow constructed wetlands as green facades and gardens for on-site greywater treatment in buildings: Two-year mesocosm study on removal performance

This study focuses on the performance and clogging of vertical flow constructed wetlands (VFCWs) planted with climbing ornamentals and ornamental plants for greywater treatment, after two years of operation at mesocosm level. Different substrate (sand, vermiculite) and vegetation (Trachelospermum jasminoides, Lonicera japonica, Callistemon laevis) types were evaluated to determine the optimal removal of pollutants. Results revealed that, during the second year of operation, removal efficiencies of turbidity and COD were significantly higher (1st year: 54-94 %; 71-89 %, 2nd year: 82-98 %; 86-95 %, respectively) for both studied planted substrates, compared to the first year. Moreover, it was found that sand systems from each studied plant as well as from the unplanted systems, were more effective compared to vermiculite for most of the studied parameters (turbidity, TSS, COD, anionic surfactants, pathogens). Sand systems were also quite effective in removing total coliforms (5 log reduction) and Escherichia coli (4 log reduction). At the end of the two-year experiment, all planted systems with sand had significantly higher hydraulic conductivity than the unplanted ones. With reference to evapotranspiration, even though planted systems had significantly higher losses, C. laevis systems demonstrated less water losses than the other vegetated systems. According to the findings, the studied plants managed to continue growing without facing added stress. Therefore, the application of climbing and ornamental plants in VFCWs for greywater treatment in buildings seems a promising option for developing green infrastructures in urban areas and enhancing the removal efficiency of such systems.

Hydrodynamics and effect of velocity on particle filtration due to bridging in water-saturated porous media using CFD-DEM simulation

Particle bridging owing to the confinement of the pore structure affects the transport and retention of particles in porous media. Particle motion driven by gravities were well investigated, whose filtration is mainly affected by the ratio of the particle diameter to the pore throat size of the medium. However, particles whose motions are driven by the fluid is essential to be investigated for particle separation from the carrying fluid. In this study, the motion of particles was driven by the liquid when passing through a water-saturated porous medium. The fluid-particle flow in a porous medium was modeled using computational fluid dynamics-discrete element method. The motion of particles in the slurry was traced in the porous medium, which enabled particle clogging to be directly precited by the interaction between the particles and pore surfaces by assessing the exact location of each particle. The pressure and flow field of the liquid were investigated, and the variation in flow path owing to particle clogging was predicted. The hydrodynamic study also showed that the Stokes number and particle concentration determined the particle clogging at the pore throats of the porous medium. Increasing the fluid velocity of particles such that the Stokes number was almost equal to 1 increased the separation efficiency of particles. Further increasing the fluid velocity reduced the residence time, which reduced the separation efficiency of the particles.

Spatial-temporal clogging development in leachate collection systems of landfills: Insight into chemical and biological clogging characteristics

The clogging of leachate collection systems (LCSs) is a typical challenge for landfills operation. Although clogging occurs in different LCS components, its spatial-temporal distributions remain unclear. This study aimed to systematically investigate the dynamic clogging development in simulated LCSs by monitoring changes in clogging characteristics over time. Results revealed that clogging accumulated in all components of the simulated LCS during a 215-day period, including chemical clogging and bio-clogging. Distinct spatial variations in clogging components were observed along the leachate flow of the simulated LCS, with the geotextile being severely clogged due to bio-clogging (70.1 ± 3.0%-80.0 ± 0.5%). Additionally, chemical clogging mainly occurred at the top (85.4 ± 0.8%-95.0 ± 0.9%) and middle (91.2 ± 0.8%-94.9 ± 1.1%) gravel layers. Nevertheless, the percentage of chemical clogging decreased from 72.0 ± 2.1% (day 42) to 42.5 ± 2.7% (day 215) at the bottom gravel layer. Chemical clogging was the main type in the pipe, accounting for 69.6 ± 0.5% (day 215). In addition, the ratios of bio-clogging to chemical clogging changed over time in all LCS components. The spatial-temporal characteristics of clogging across LCS components can enhance the understanding of clogging mechanisms, facilitate the design optimization of LCSs, and promote the formulation of effective control strategies.

Dynamics and control mechanisms of inorganic nitrogen removal during wetting-drying cycles: A simulated managed aquifer recharge experiment

Managed aquifer recharge (MAR) systems can be operated intermittently through wetting-drying cycles to simultaneously improve the water supply and quality. Although MAR can naturally attenuate considerable amounts of nitrogen, the dynamic processes and control mechanisms of nitrogen removal by intermittent MAR remain unclear. This study was conducted in laboratory sandy columns and lasted for 23 d, including four wetting periods and three drying periods. The hydraulic conductivity, oxidation reduction potential (ORP), and leaching concentrations of ammonia nitrogen and nitrate nitrogen of MAR systems were intensively measured to test the hypothesis that hydrological and biogeochemical controls play an essential role in regulating nitrogen dynamics at different stages of wetting-drying cycles. Intermittent MAR functioned as a sink for nitrogen while providing a carbon source to support nitrogen transformations; however, it occasionally became a source of nitrogen under intense flushes of preferential flow. Nitrogen dynamics were primarily controlled by hydrological processes in the initial wetting phase and were further regulated by biogeochemical processes during the subsequent wetting period, supporting our hypothesis. We also observed that a saturated zone could mediate nitrogen dynamics by creating anaerobic conditions for denitrification and buffering the flush effect of preferential flow. The drying duration can also affect the occurrence of preferential flow and nitrogen transformations, which should be balanced when determining the optimal drying duration for intermittent MAR systems.

Efficient carbon removal and excellent anti-clogging performance have been achieved in multilayer quartz sand horizontal subsurface flow constructed wetland for domestic sewage treatment

The present study aimed to investigate the application of a multilayer quartz sand substrate horizontal subsurface flow constructed wetland (HSFCW) for campus sewage treatment. It aimed to assess the pollutant removal efficiency and anti-clogging performance under the suggested maximum organic loading rate (250 g/m²/d). The results of the multilayer HSFCW (CW6) were compared to the mololayer HSFCW (CW1) for the removal of the chemical oxygen demand (COD), solid accumulation, and microbial communities. During operation, the combination conditions of high hydraulic loading rate (HLR) with low COD concentration were better for COD removal under a high organic loading rate (OLR) of 200-300 g/m²/d. The maximum removal rate reached 80.4% in CW6 under high HLR, which was 13.8% higher than that in CW1, showing better adsorption and biodegradation ability of organic matter. Impressive clogging resistance capacity was found in CW6 due to the lower contents of the insoluble organic matter (IOM) that are prone to clogging, indicating full degradation of organic matters, particularly IOM, in CW6 under high HLR. Less abundance of unclassified Chitinophagaceae (under low HLR), Pedobacter and Saccharibacteria_genera_incertae_sedis (under high HLR) in CW6, which contributed to aerobic membrane fouling, helped to prevent clogging. Moreover, Brevundimonas, Cloacibacterium, Citrobacter, Luteimonas contributed to IOM degradation, thus further enhancing the anti-clogging performance. In view of the better clogging resistance performance, the application of CW6 operated under high HLR and low COD concentrations was recommended to achieve economical, efficient, and steady COD removal for domestic sewage treatment in long-term operation.

Applying lysozyme, alkaline protease, and sodium hypochlorite to reduce bioclogging during managed aquifer recharge: A laboratory study

Alleviating bacterial-induced clogging is of great importance to improve the efficiency of managed aquifer recharge (MAR). Enzymes (lysozyme and alkaline protease) and sodium hypochlorite (NaClO) are common biological and chemical reagents for inhibiting bacterial growth and activity. To investigate the applicability of these reagents to reduce bioclogging, percolation experiments were performed to simulate a weak alkaline recharge water infiltration through laboratory-scale sand columns, with adding 10 mg/L lysozyme, alkaline protease, and NaClO, respectively. The results showed that, with the addition of lysozyme, alkaline protease, and NaClO, the average clogging rates (the reduced percentages of relative saturated hydraulic conductivity of the sand columns per hour during the percolation experiments) were 0.53%/h, 0.32%/h and 0.06%/h, respectively, which were much lower than that in the control group (0.99%/h). This implied that bioclogging could be alleviated to some extent following the treatments. For further analyzing the mechanisms of the regents on alleviating bioclogging, the bacterial cell amount and extracellular polymeric substances (EPS) concentration were also measured to study the effects of lysozyme, alkaline protease, and NaClO on bacterial growth and EPS secretion. Lysozyme and alkaline protease could disintegrate bacterial EPS by hydrolyzing polysaccharides and proteins, respectively, while they had little effect on the bacterial cell amount. The addition of NaClO significantly decreased the bacterial cell amount (P < 0.05) and thus greatly alleviated bioclogging. Although the lowest average clogging rate was achieved in the NaClO group, it can generate disinfection by-products that are potentially harmful to the environment and human health. Therefore, the biological-based method, i.e., enzyme treatment, could be a promising option for bioclogging control. Our results provide insights for understanding the mechanisms of lysozyme, alkaline protease, and NaClO to alleviate bioclogging, which is of great importance for addressing the clogging problem during MAR activities and achieving groundwater resources sustainable utilization.

Application of loofah and insects in a bio-trickling filter to relieve clogging

Bio-trickling filters (BTFs) use an inert filler to purify pollutants making them prone to clogging due to bacterial accumulation. To investigate the performance of a non-inert filler in BTF and its cooperation with insects to relieve clogging, a vertical BTF was constructed with a loofah/Pall ring/polydimethylsiloxane composite filler and selected bacteria to purify toluene. The BTF was started up within 17 d and restarted within 3 d after starvation for 12-16 d. Its average removal efficiency was >90% at steady state. The maximum elimination capacity of 86.4 g·(m³·h)^-1 was obtained at a volume capacity of 96.2 g·(m³·h)^-1. The introduction of holometabolous insects (Clogmia albipunctata) rapidly removed the biofilm and accelerated the degradation of the loofah, which alleviated clogging. Furthermore, confocal laser scanning microscope (CLSM) observations showed that the biofilm polysaccharides were difficult to remove, while lipids were readily lost. Analysis of microbial diversity over time and space revealed that the dominant bacterium, Comamonas, was replaced by diverse microflora with no obvious dominant genus. Insect introduction and loofah migration had little effect on the evolution of microflora. This study provides a promising approach to operating BTFs with less clogging.

Spatiotemporal difference of leachate production and its impact on the development and dynamics of LCS clogging

Due to the complexity of industrial solid waste, heavy metals and organics can be enriched in leachate. While leachate is difficult to handle, it can also cause clog of the leachate collection system (LCS), increasing the risk of leakage. Therefore, it is necessary to study the clogging process of LCS in industrial solid waste landfills (ISWLs). In this study, the prediction of the clogging process and hydraulic conductivity evolution of the LCS in ISWL were carried out through laboratory experiments and model simulations. The results show that the LCS of ISWLs in China faces severe clogging challenges. First, the rate of clogging is inversely proportional to the rate of leachate production. Then, it was found that the main influencing factor was infiltration conditions (precipitation and capping systems). Under accelerated infiltration conditions, the time for complete clogging of the leachate drainage pipes was shortened from the initial 26-735 years to 11-315 years. The time to complete LCS clogging was shortened from the initial 78-2205 years to 32-945 years. In addition, the acceleration of the clogging process was fully consistent with the increase in leachate production. In particular, when the net infiltration volume increases from 0 to 50 mm, the clogging process is significantly accelerated. After greater than 50 mm, the effect on the clogging process gradually decreases. This provides a reliable theoretical basis for accurately predicting the clogging process of LCS.

Anti-clogging mechanism of freeze-thaw combined with step vacuum preloading in treating landfill sludge

Globally, landfill sludge (LS) has accumulated in large quantities, and its reduction and dewatering are urgently needed. To address pollution problems and clogging of drainage boards caused by chemical conditioning combined with traditional vacuum preloading (TVP), a freeze-thaw combined with step vacuum preloading (F/T-SVP) method is proposed. A comparative experimental study was carried out between TVP and SVP to explore the anti-clogging mechanism of F/T-SVP in treating LS. As a result, the water discharge for the original sludge (OS) is 1840 ml, the water discharge for TVP is 8830 ml and for SVP is 10,010 ml; The total settlement of SVP is 16% higher than that of TVP; TVP has a volume reduction ratio of 57.6%, while SVP has 66.8%; the OS's water content was 86%, which was reduced to 57.6% by F/T-SVP; The center of the drainage board of TVP is seriously clogged, while the particles of SVP are evenly distributed; The tendency for small particles to undergo transport is relatively low at the beginning of SVP, which can effectively reduce clogging; TVP mainly focuses on the compression of large pores into small pores, and SVP mainly focuses on the compression of large into small pores and micropores. In SVP, there is more consolidation and a more compact structure. When F/T-SVP is used to treat LS, the pores are gradually penetrated, effectively avoiding the generation of clogging and improving LS's drainage and consolidation.

Impact of clogging on accumulation and stability of phosphorus in the subsurface flow constructed wetland

Substrate clogging is one of the major operation challenges of subsurface flow constructed wetlands (SSF-CWs). And the phosphorus (P) removal performance and stability of P accumulation of SSF-CWs would be varied with the development of substrate clogging. In this study, three horizontal SSF-CWs microcosms with different clogging degrees were conducted to explore the mechanism of P accumulation behavior influenced by substrate clogging. Increase in clogging degree resulted in hydraulic retention time (HRT) diminution and adsorption sites increase, which jointly led to reduced P removal efficiency at low clogging degree (L-CW), however, higher P removal efficiency was obtained as adsorption sites increase offset HRT diminution at high clogging degree (H-CW). Substrate adsorption was the primary removal pathway in all SSF-CW systems. It accounted for 77.86 ± 2.63% of the P input in the H-CW, significantly higher than the control (60.08 ± 4.79%). This was attributed to a higher proportion of Fe/Al-P accumulated on the substrate of H-CW, since clogging aggravated the anaerobic condition and promoted the generation of Fe ions. The increase in clogging degree also elevated the release risk of the accrued P in SSF-CWs, since Fe/Al-P was considered bioavailable and readily released under environmental disturbance. The obtained results provide new insights into the P transport and transformation in SSF-CWs and would be helpful to optimize substrate clogging management.

Influence of the injection of densified polymer suspension on the efficiency of DNAPL displacement in contaminated saturated soils

Nowadays the remediation of DNAPL contaminated zones near groundwater has gained great prominence in environmental fields due to the high importance of water resources. In this work, we suggest injecting a densified polymer suspension by adding barite particles to displace DNAPL. To evaluate the efficiency of the densification of polymer suspensions on the displacement of DNAPL, various densities of barite-polymer suspension; lower, equal, and higher than the density of DNAPL were prepared and their rheological behavior was analyzed. Then flow experiments were performed using a decimetric-scale 2D tank. The displacement procedure was monitored with an imaging technique and the production and injection process data were recorded by mass balance interpretation. It was shown that the densification of the polymer suspension could improve the displacement efficiency of DNAPL up to four times. The clogging behavior of barite-polymer suspension was assessed in a 1D column. Generalized Darcy's law and the continuity equation were used to numerically simulate the experimental two-phase flow. To take into account the clogging behavior of the suspension, the transport equation of diluted species was implemented into the model. The simulation results show that the model can properly predicts the experimental consequences.

Measurement of pore volume, connectivity and clogging of pervious concrete reactive barrier used to treat acid mine drainage

It has recently been shown that pervious concrete is a promising, effective technology as a permeable reactive barrier system for treatment of acid mine drainage (AMD). However, pore clogging also occurs simultaneously during AMD treatment. In the present study, mixtures of pervious concrete were made and used in a column experiment during which pore clogging occurred in the samples. Pore volume, connectivity and other parameters of pervious concrete were evaluated using five (5) different methods comprising the volumetric method (VM), linear-traverse method (LTM), image analysis (IA), falling head permeability test and X-ray microcomputed tomography. It was found that pervious concrete effectively removed from AMD, about 90 to 99% of various heavy metals including Al, Fe, Zn, Mn and Mg. Cr concentration significantly increased in the treated effluent, owing to leaching from cementitious materials used in mixtures. The VM and LTM gave statistically similar pore volume results, while IA's values were 20 to 30% higher than those of the conventional methods. The falling head permeability test and IA were found to be effective in quantifying pore clogging effects. Pervious concrete exhibited high pore connectivity of 95.0 to 99.7%, which underlies its efficacious hydraulic conductivity.

An approach for the scalable production of macroporous polymer beads

A tubular co-flow reactor to produce macroporous polymer beads by polymerization of medium and high internal phase emulsion (M/HIPE) templates was developed. This reactor allows for improved production rates compared to tubing based microfluidic devices. Water-in-oil (W/O) M/HIPEs, containing methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) monomers in the continuous phase, were injected into a re-circulating carrier phase. The continuous phase of the emulsion droplets was UV polymerized in situ, resulting in polyM/HIPE beads. The emulsion composition was adjusted to produce poly(MMA-co-EGDMA) porous polymer beads with a protective crust and an interconnected internal pore structure. HCl loaded beads were produced by adding the active ingredient into the dispersed emulsion phase, leading to HCl encapsulation in the porous structure of the beads after polymerization. Even after exposure to ambient conditions for 24 h, 60% of the HCl remained in the beads, indicating good encapsulation efficiencies. Thus, it is possible to use such macroporous beads as delivery vehicles.

Sustaining low pressure drop and homogeneous flow by adopting a fluidized bed biofilter treating gaseous toluene

A biofilter treating gaseous VOCs is usually a packed bed system which will encounter bed clogging problems with increased pressure drop and uneven gas flow in the filter bed. In this study, a lab-scale fluidized bed reactor (FBR) was set up treating gaseous toluene and compared with a packed bed reactor (PBR) with the same bed height of 150 cm. During 45 days of operation, the average elimination capacity of the FBR was 242 g m^-3∙h^-1, similar to that in the PBR (228 g m^-3∙h^-1) under an inlet toluene concentration of 100-300 mg m^-3 and an empty bed residence time (EBRT) of 0.60 s. A better mass transfer was also confirmed in the FBR by molecular residence time distribution measurement. The pressure drop of the PBR increased dramatically and exceeded 8000 Pa m^-1 while that of the FBR maintained approximately 200 Pa m^-1. On the 40th day, the air flow distribution in the FBR was more homogeneous than that in the PBR. The differences in pressure drop and air flow distribution were due to a much lower and more uniform distribution of biomass in the FBR than that in the PBR. The detached biomass collected from the off-gas of the FBR was almost 13 times of that from the PBR. Similar microbial community structures were observed in both systems, with the dominant bacterial genus Stenotrophomonas and the fungal genera Meyerozyma, Aspergillus. The results in this study demonstrated that the FBR could achieve a more stable performance than a PBR in long-term operation.

Fabrication of anti-scaling HDPE/fluorinated acrylate polymer/nano-silica composite for landfill leachate piping system

Clogging generally happens to the leachate piping system, which poses a risk to the environment. A low surface energy nanocomposite is prepared to mitigate the cloggings, by adding the fluorinated acrylate polymer and hydrophobically modified nano-silica into high-density polyethylene (HDPE) substrate. The best addition of the fluorinated acrylate polymer and the nano-silica is given as 15% and 5%, to produce the composite with a low surface energy of 29.4 mJ/m². Through the characterization of contact angle (CA), electrochemical corrosion, scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS), atomic force microscope (AFM) and thermogravimetry (TG), the composite shows low wettability, good corrosion resistance and thermal stability. The surface hydrophobic property of the composite remains unchanged after being immersed in an acidic (pH = 2) and an alkaline (pH = 12) solution, indicating that the prepared composite has strong adaptability to the extreme environments. In addition, the composite shows better anti-scaling performance than that of the commercial high-density polyethylene (HDPE) and polyvinyl chloride (PVC) pipe materials by application of a dispensing leachate immersion test. The results provide insights into engineering practice for the design and manufacture of pipe materials for leachate collection and transport.

Efficacy and complications of regional citrate anticoagulation during continuous renal replacement therapy in critically ill patients with COVID-19

Background

We compared filter survival and citrate-induced complications during continuous renal replacement therapy (CRRT) with regional citrate anticoagulation (RCA) in COVID-19 and Non-COVID-19 patients.

Methods

In this retrospective study we included all consecutive adult patients (n = 97) treated with RCA-CRRT. Efficacy and complications of RCA-CRRT were compared between COVID-19 and Non-COVID-19 patients.

Results

Mean filter run-time was significantly higher in COVID-19 patients compared to Non-COVID-19 patients (68.4 (95%CI 67.0–69.9) vs. 65.2 (95%CI 63.2–67.2) hours, respectively; log-rank 0.014). COVID-19 patients showed significantly higher activated partial thromboplastin time (aPTT) throughout the CRRT due to intensified systemic anticoagulation compared to Non-COVID-19 patients (54 (IQR 45–61) vs. 47 (IQR 41–58) seconds, respectively; p < 0.001). A significantly higher incidence of metabolic alkalosis, hypercalcemia and hypernatremia, consistent with reduced filter patency and citrate overload, was observed in COVID-19 patients compared to Non-COVID-19 patients (19.1% vs. 12.7%, respectively; p = 0.04). These metabolic disarrangements were resistant to per-protocol adjustments and disappeared after replacement of the CRRT-filter.

Conclusions

RCA-CRRT in COVID-19 patients with intensified systemic anticoagulation provides an adequate filter lifespan. However, close monitoring of the acid-base balance appears warranted, as these patients tend to develop reduced filter patency leading to a higher incidence of citrate overload and metabolic disturbances.

Trial registration (local authority)

EA1/285/20 (Ethikkommission der Charité - Universitätsmedizin Berlin); date of registration 08.10.2020.

Improving the performance of vertical flow constructed wetlands by modifying the filtering media structure

The aim of this research was to study the influence of the bed media configuration and particle size on the treatment efficiency of subsurface vertical flow (VF) constructed wetlands (CWs) treating municipal wastewater. Two outdoor pilot units (VF1 and VF2, planted with Phragmites australis) with the configuration C1 were operated in parallel for 2 years at similar surface loading rates of 9.7 ± 3.2 (VF1) and 10.1 ± 3.3 (VF2) g biological oxygen demand (BOD₅)/m²·day (19.5 ± 6.4 (VF1) and 20.4 ± 6.2 (VF2) g chemical oxygen demand (COD)/m²·day). A different configuration C2 was used during the third year at 16.9 ± 4.6 (VF1) and 18.2 ± 3.0 (VF2) g BOD₅/m²·day and 26.0 ± 7.2 (VF1) and 28.0 ± 4.7 (VF2) g COD/m²·day. Two different filtering materials (1-3-mm sand for VF1 and 2-6-mm fine gravel for VF2) were used for configuration C1. The same units were modified after 2 years of operation by adding a 10-cm layer of fine sand (0-2 mm) on the top (configuration C2). In C1 conditions, the unit with the coarse material VF2 showed significantly (p < 0.05) lower removal efficiencies of total suspended solids (TSS) and BOD₅ than VF1, and both units failed to meet the BOD₅ discharge limit. In C2 conditions, removal efficiencies reached 82% TSS, 97% BOD₅, 76-81% ammonia, and 60-66% TN, without significant differences between VF1 and VF2 units. Removal efficiencies were significantly higher for configuration C2 than that for C1, due to the positive effect of the upper fine sand layer. The presence of this fine sand layer doubled the water retention time and increased the removal rates, while the infiltration rates were high enough for an operation free of clogging.

Assessing maintenance techniques and in-situ pavement conditions to restore hydraulic function of permeable interlocking concrete pavements

Permeable pavements are increasingly implemented to mitigate the negative hydrologic outcomes associated with impervious surfaces. However, the hydraulic function of permeable pavements is hindered by clogging in their joint openings, and systematic maintenance is needed to ensure hydraulic functionality throughout the design lifespan of these systems. To quantify the effectiveness of various maintenance measures, surface infiltration rates (SIRs) were measured before and after five different maintenance techniques were applied to five permeable interlocking concrete pavements (PICPs) in central Ohio, USA. Three maintenance techniques, the Municipal Cleaning Vehicle (MCV), the Rejuvenater, and a pressure washer and the Rejuvenater performed in series, significantly improved median SIRs from 16 to 26, 5 to 106, and 11 to 37 mm/min, respectively. However, pressure washing alone resulted in no significant difference to PICP SIR (median SIRs increased from 8 to 20 mm/min). Regenerative air street sweeping significantly worsened SIRs when performed during wet weather (median SIRs decreased from 19 to 4 mm/min) but had no significant impact on SIRs during dry weather (median SIRs decreased from 21 to 18 mm/min). This work captured the maintenance effectiveness of two techniques for the first or second time, namely the Rejuvenater and MCV, to investigate their use as a suitable maintenance technique. Further, the maintenance techniques were tested on multiple PICPs, thus the effect of in-situ pavement conditions had on hydraulic improvement via maintenance could be addressed. Differences in general upkeep, traffic, and runoff routed to a PICP affected the depth of clogging below the pavement surface, which forestalled hydraulic improvement. Though shown to improve the SIR of PICP systems, results indicate that the maintenance techniques were not capable of restoring pavement hydraulics to initial conditions. These results demonstrate the need for regular, routine maintenance and topping up of joint aggregate before clogging migrates deeper into the pavement profile.

Study on clogging mechanisms of constructed wetlands from the perspective of wastewater electrical conductivity change under different substrate conditions

Constructed wetland (CW) has obvious advantages in wastewater treatment of medium and small towns. However, there is a lack of health monitoring research on CW system clogging. The electrical conductivity (EC) of wastewater purified by CW is related to the concentration of pollutants, which can reflect the CW clogging. The objectives of this study are to reveal the mechanisms of CWs substrate clogging from the perspective of wastewater EC changes, and provide an important reference for the health evaluation of CWs. The EC changes of nine CWs substrates (quartz sand, zeolite, gravel, coarse sand, straw biochar, sludge biochar, clay ceramsite, fly ash ceramsite and shale ceramsite) under different conditions (purified water, wastewater and wastewater + NaCl) were tested, and comparative analysis was used to reveal the influence of different substrate materials on the change of wastewater EC. The results show that the adsorption ability of substrate material isn't the main factor affecting the EC of wastewater, and the soluble component in the material is the important factor to cause the difference of EC increment. Under the condition of 0.4-1.0 g L^-1 NaCl concentration, the adsorption of substrate materials had little effect on the EC of wastewater, and the effect of NaCl used in CW tracer experiment was good. Quartz sand, coarse sand, gravel and sludge biochar have little influence on the change of wastewater EC. Other materials that have great influence on the change of wastewater EC can be treated by modifying or controlling the mixing ratio. The results are of great significance to reveal the clogging state of CW system and to carry out health assessment research.

A new technique of seawater intrusion control: development of geochemical cutoff wall

The construction of a subsurface dam and/or physical cutoff barriers is one of the most known techniques used to prevent seawater intrusion during excessive exploitation of freshwater from a coastal aquifer. This method is widely used in many sites around the world (Japan, Brazil, India, Burkina Faso…). In this study, we present an innovative technique for constructing subsurface barriers based on geochemical reactions. A calcite cutoff wall is developed by mixing two aqueous solutions Na₂CO₃ and CaCl₂ under pCO₂ equal to 3.16·10^-4 bar. The deposition of calcite in the mixing zone induces a high clogging, which greatly reduces the porosity and then the permeability of the aquifer into the injection zone. We use GEODENS code to study the effect of a developed geochemical cutoff wall on saltwater intrusion and to assess their protective effect on preventing seawater intrusion. The GEODENS code can solve these equations by a finite element procedure; it can handle density-dependent flow, transport, and geochemical reactions in porous media. The effect of depth and location of the geochemical cutoff wall is tested and results showed a significant reduction of seawater intrusion penetration length. According to the budget used in many barrier construction projects, we have shown that the developed geochemical cutoff wall presented in this work could produce a lower seawater intrusion penetration length than the traditionally used barriers at a very lower cost.

A Safe Way to Administer Drugs Through a Nutrition Tube-The Simple Suspension Method

The simple suspension method (SSM), developed by Kurata in 1997, is a way to suspend tablets and capsules in warm water for decay and suspension prior to their administration. This method is safe and has various advantages such as the avoidance of tube clogging and the loss of the drug. This study aimed to investigate whether a higher percentage of commonly used drugs could pass through nutrition tubes effectively using SSM, relative to that using the conventional crushing method. A tablet or capsule was inserted into a 20 mL syringe with warm water (at 55 °C). After 10 min, it was shaken in the syringe. The suspension liquid was injected into tubes of the following sizes: 8 Fr, 10 Fr, 12 Fr, 14 Fr, 16 Fr, and 18 Fr. A total of 3686 tablets and 432 capsules that are frequently used in Japan were tested. Using SSM, 3377 (91.6%) tablets and 359 (83.1%) capsules disintegrated within 10 min and passed through the tube without clogging it in the tube passage test. With the conventional crushing method, 2117 tablets (57.4%) and 272 capsules (63.0%) could be crushed. SSM reduced the risk of tube clogging and drug loss with more drugs than that with the conventional crushing method. The number of drugs indicated for administration by SSM is greater than that indicated by the conventional crushing method. Further studies are needed to consider its utility compared to conventional methods for dysphagia patients in clinical settings.

Evaluation of wastewater treatment performance to a field-scale constructed wetland system at clogged condition: A case study of ammonia manufacturing plant

Assessment of the treatment performance in the field-scale hybrid constructed wetland (CW) for ammonia manufacturing plant remains limited. After being in operations running on and off since 2014, the hybrid CW which treats effluent from the ammonia manufacturing plant in Peninsular, Malaysia has recently demonstrated the full clogging to the CW. It takes only 8 months to demonstrate a big deterioration of performance in 2019. Though the mechanism of clogging is not clear, which can be partially from inherent design problems or operational issues, nonetheless, it is important to evaluate how this clogging has impacted the effluent treatment performance and the continuous utilization of the CW. The purpose of this study is to evaluate the impact of the treatment performance on the ammoniacal nitrogen and COD removal when the CW is clogged. The result revealed that there is no impact on COD removal, but it has a substantial impact on the ammoniacal nitrogen removal. The ammoniacal nitrogen removal dropped to negative (outlet concentration is higher than inlet concentration) during the clogged period. Another observation is, the low removal rate also coincides with a high COD/N ratio, when the COD/N ratio increased to >2, the ammoniacal nitrogen removal rate dropped substantially, with the coefficient of determination, R² of 40.5%. The root cause for the clogging to develop in a short period of time is unidentified. However, it is still worth noting that COD and ammoniacal nitrogen efficiency did not behave the same at the clogged CW.

Calcium leaching characteristics in landfill leachate collection systems from bottom ash of municipal solid waste incineration

Calcium leaching is a critical factor in the clogging of leachate collection systems (LCS), a phenomenon that affects landfill stability and operation. The bottom ash (BA) of municipal solid waste (MSW) incineration plants contains large quantities of calcium-based compounds. Landfilling is the main disposal method for BA in China that intensifies the consequences of LCS clogging. The factors influencing BA calcium leaching were investigated using simulated leachate. The results showed that fine BA particles, low pH values, high temperature, and ratios of leachate to BA solids were conducive to calcium leaching. Calcium leaching was found to be higher in actual leachate than in simulated leachate. At pH = 5, the cumulative calcium dissolution ratios (CDRs) were 83.36% and 31.49% after 20 days of leaching in the actual and simulated leachate, respectively; at pH = 6, the values were 50.67% and 12.06%, respectively. The introduction of landfill gas could decrease the calcium dissolution and leaching rates. When the ratio of leachate to BA solid was 20:1 mL/g, the accumulative CDR values were 45.98% (pH = 6) and 5.80% (pH = 8) without landfill gases, and 4.59% (pH = 6) and 0.48% (pH = 8) with landfill gases. These results provide the scientific basis for clogging risk prediction with respect to calcium leaching in the LCS of landfills. BA landfilling in old landfill areas with relatively high leachate pH and low chemical oxygen demand, as well as when leachate mixed with an appropriate amount of landfill gases, could be feasible measures to reduce calcium leaching and further prevent clogging in LCS.

Managing biofilm growth and clogging to promote sustainability in an intermittent sand filter (ISF)

The sustainability of rural sanitation includes the long-term welfare of both rural and urban societies. As a commonly used rural sanitation technology, operation of intermittent sand filters (ISF) is impacted by biofilm clogging inside the ISF. In this study ISF performance is studied at low hydraulic loading rates (HLR) to explore the interaction between biofilm growth and wastewater treatment efficiency. CW2D/HYDRUS, a simulation model which does not include media hydraulic property changes caused by biofilm growth, is utilized as a numerical control to contrast the effects of biofilm growth inside an experimental ISF. A paired experiment with simulation demonstrate that biofilm clogging comprised dominantly of heterotrophs occurred in the top layers of the ISF. Lowered HLR slows clogging development but not final clogging extent. The biofilm clogging development zone offers adequate removal of applied biodegradable COD and NH₄⁺ - N. However, the spatial distribution of heterotrophs and biodegradable COD does not match the denitrification requirement of the resulting NO₃^- - N. A simultaneous nitrification and denitrification (SND) potential is manifested in the clogging development zone, but lowered HLR reduces media moisture level to a less favorable level for denitrification. Furthermore, slowed water movement under lower HLR aggravates the accumulation of NO₃^- - N, which can potentially result in counterproductive salt accumulation. Since biofilm growth is a natural and self-adaptive response to wastewater application, this study suggests accepting limited, managed biofilm growth and clogging in ISFs. In addition, this study calls for further research to manage biofilm growth and clogging for long-term ISF sustainability.

Mechanism and dynamic evolution of leachate collection system clogging in MSW landfills in China

When the leachate collection system (LCS) clogged, the accumulated leachate mound within the landfill will rise both the disposal operation safety and groundwater contamination risks, which is a common phenomenon in China. In our previous studies, geotextile filtration tests and a set of simulated column experiments were conducted to investigate the physical and biochemical clogging mechanisms, respectively. To evaluate the LCS failure development in the long term, in this study, based on the field investigations and above experiments, a comprehensive finite element numerical model was developed to predict the LCS clogging and leachate accumulation. Results showed that the LCS in China was facing serious clogging challenges. Due to the larger size and higher concentration of particle matter in raw leachate, the pores of the nonwoven geotextile were clogged by it over a shorter period than designed. Meanwhile, under the assistance of biological and biochemical clogging, the hydraulic conductivity of the geotextile layer decreased to 10^-8-10^-9 (m/s) over 1-2 years and resulted in leachate accumulation within the waste layer. In contrast, the gravel layer clogging was dominated by biochemical reactions, which were relatively slow but continuously. When the gravel layer was completely clogged after 17 years of simulated operation, the stagnated leachate mound inside the landfill body and the leachate head on the bottom liner would both rise to the unacceptable height. Therefore, the LCS clogging should be fully considered in municipal solid waste (MSW) landfill design and operation in China.

Accumulation and characteristics of fluorescent dissolved organic matter in loess soil-based subsurface wastewater infiltration system with aeration and biochar addition

Subsurface wastewater infiltration systems (SWISs) have been widely used to treat rural domestic sewage. However, the low nitrogen removal and severe clogging problem always restrict the sustainability of SWISs for wastewater treatment. This study investigated the effects of aeration and biochar on the accumulation of nutrients and dissolved organic matter (DOM) in the substrate of loess soil-based SWISs for understanding the accumulation characteristics of DOM and the enhanced decontamination mechanism. The results showed that biochar addition could not improve the accumulation of nitrogen and phosphorus in the substrate, but could enhance denitrification (22%) via providing sufficient carbon for microorganisms. Moreover, the accumulation of organic matter in the substrate was also greatly affected. The DOM concentration of System D in the 40-60 cm layer reached 85.76 mg L^-1, which indicated that biochar could release abundant DOM. Substrate DOM mainly contained humic acid-like and tryptophan-like substances. Moreover, the refractory macromolecular DOM components with high aromaticity and humification were found in the substrate below 60 cm of systems with biochar addition. This may be related to the DOM released by biochar and the extracellular polymeric substance (EPS) produced by microorganisms. It may affect the sustainability of the substrate to a certain extent, but fortunately that intermittent aeration could reduce this adverse effect. This research could provide new insights for preventing clogging and useful guidance for improving wastewater treatment performance in SWISs.

Assessment of clogging of permeable pavements by measuring change in permeability

Permeable pavements are a common solution for stormwater management. Porous areas in the pavements allow water to percolate into the subsurface layers, reducing surface runoff. However, it is common for substances to clog the voids, decreasing the porous area and permeability of the pavement system. This study examined the change in permeability over time at a site with two permeable pavement systems, the JW Eco-technology (JW) and pervious concrete (PC). Square frames SF-4 and SF-9 were used to perform falling-head and constant-head permeability tests, respectively. Results show that JW had a similar permeability across the test locations, 6.27-7.64 cm/s when using SF-4, and 0.95-1.00 cm/s when using SF-9. While the permeability at the center locations of PC showed no significant loss of permeability, there was a significant reduction of permeability on the corner and edge areas, where permeability ranged 0.28-1.73 cm/s using SF-4 and 0.14-0.36 cm/s using SF-9, suggesting the occurrence of clogging over time at corner locations. Furthermore, the measured values highlighted the measurement variability in permeability between the falling-head based method and the constant-head method, with measurements from SF-4 being approximately 6.2-7.6 and 2.0-5.7 times higher than those from SF-9 on JW and PC, respectively. In addition, as no current literature quantifies the relationship between permeability and extent of clogging for the JW Eco-technology pavement, evaluation of the proportionate change in permeability with respect to voids, or individual aqueducts, of JW pavement were investigated. While not a 1:1 linear relationship, data indicate that the permeability increased with an increase in non-blocked aqueducts. The JW pavement maintained more than 50% of its capacity when half of the aqueducts were fully blocked. Even when only one aqueduct was clear from clogging, the system had 36% (SF-4) and 19% (SF-9) of maximum permeable capacity.

Effects of clogging on ultrasonic transmission through saturated granular single and double porosity media

The clogging caused by the deposition of suspended particles modifies in depth several mechanical parameters (permeability, porosity, bulk moduli, etc.) of porous media and influences the acoustic behaviour. Consequently, at a fixed position in the medium, changes in phase velocity and attenuation are observed in the amplitude of the temporal signal of the transmitted waves. In this work, ultrasonic techniques are presented both for detecting and measuring the clogging in a water saturated porous medium. The acoustic measurements from the clogged samples are compared with the deposition profiles obtained at the end of injection experiments. Moreover, links are established between on the one hand phase velocity and the total porosity, and on the other hand the transmitted signal energy and the variation of porosity as consequence of particle deposition.

Assessment of clogging of managed aquifer recharge in a semi-arid region

To overcome water scarcity issues in arid and semi-arid regions, Managed Aquifer Recharge (MAR) remains a viable and suitable solution to manage and restore aquifers. However, clogging represents a major issue that can affect the durability and efficiency of MAR structures. The aim of this study was to evaluate the extent of clogging in MAR sites (Berrechid, Morocco). To achieve this objective, two field-based studies were undertaken: the first one consists of implantation of sand-filled columns in the recharge sites to evaluate the surface and subsurface clogging. The second one consists of the implantation of pickets over a 750 m² area in each recharge site to measure the extent of deposit thickness on the surface of the wadi bed. Results show that, despite the low rainfall (<1.4 mm/day) and the short period (91 days) of the study, the deposits thickness exceeds 3 cm in a large part of the MAR. The suspended solids concentrations measured in recharge sites ranged from 1.1 to 1.4 g/L. Due to the particles retention, the estimation of the saturated hydraulic conductivity (k) of the sand declines over 90% in the immediate entrance of the columns. The k values measured in situ during the drying period ranged from 10^-5 to 10^-6 m/s. The k values of the cake formed, without cracks, was about 10^-8 m/s. The presence of cracks drives the entire infiltration. However, due to the high plasticity index of the MAR soil, a slight reduction of cracks opening during wetting cycles is observed. In addition, particles deposited in these cracks, would contribute actively to the reduction of infiltration. The results of this study clearly showed the MAR sites vulnerability in semi-arid regions due to physical clogging.

Solute transport modelling to manage groundwater pollution from surface water resources

This article provides an analytical solute transport model to investigate the potential of groundwater contamination by polluted surface water in a two dimensional domain. The clogging of streambed which makes the aquifer partially penetrated by the stream, is considered in the model. The impacts of pumping process, hydraulic conductivity and clogging layer on the quality of water produced from nearby drinking water wells are evaluated. It is found that results are consistent with numerical simulation conducted by MODFLOW software. Moreover, the model is applied using data of contamination occurrence in Malaysia, where high contaminants concentrations are found close to streams. Results show that the pumping activities (rate and time period) are crucial factors when evaluating the risk of groundwater contamination from surface water. Additionally, this study illustrates that the increase in either hydraulic conductivity or leakance coefficient parameters due to the clogging layer will enlarge the area of contamination. The model is able to determine the suitable pumping rate and location of the well so that the contamination plume never reaches the extraction well, which is useful in constructing riverbank filtration sites.

Time-domain induced polarization as a tool to image clogging in treatment wetlands

During the last decade, treatment (artificial) wetlands have flourished all over Europe for the treatment of sewages from small communities thanks to their low cost of operation. The clogging of the filter of these wetlands is an issue affecting their efficiency and considered as their main operational problem. The present work shows the results of the application of a geophysical method called time-domain induced polarization. It is used to non-intrusively image, in 3D, the clogging of the gravel filters in a quick and efficient way. Induced polarization characterizes the ability of a porous material to reversibly store electrical charges when submitted to an electrical field. The material property characterizing this ability is called normalized chargeability. A set of laboratory experiments allows to determine an empirical relationship between the normalized chargeability and the weight amount of clogging. Induced polarization measurements have been performed in the field over a treatment wetland to get a 3D reconstructed image (tomography) of the normalized chargeability. From this tomography and the previously defined relationship, we are able to image in 3D the distribution of clogging and where it is concentrated in the filter. We can therefore identify the areas requiring preventive measures to minimize this clogging issue.

Quantifying clogging patterns of infiltration systems to improve urban stormwater pollution reduction estimates

Infiltration systems are among the most commonly implemented practices to control urban stormwater and to attenuate pollutant delivery to receiving waters, because they are relatively cheap to build and amenable to space constraints in urbanized areas. However, infiltration systems tend to clog with sediments, which can rapidly reduce their performance. While clogging has been consistently identified as a significant determinant on infiltration BMP (best management practice) performance and lifespan, there have been few methods reported to predict rates of clogging or incorporate insights to urban catchment water quality modeling. We ran a series of laboratory and field experiments to identify clogging mechanisms and quantify infiltration performance declines as a function of sediment loading. The results show rapid initial declines of infiltration rate, primarily due to accumulation of material at the bottom of the infiltration BMP. The performance decline trajectories were sensitive to BMP geometry, with BMPs that had greater lateral infiltration surface area declining less quickly. We integrated these experimental results to a spatially distributed stormwater model to illustrate how they can be used to predict BMP performance declines over time and assess cost trade-offs. Results will be used to adapt algorithms in a cloud-based stormwater management platform to better inform maintenance needs for cities and improve the accuracy of urban stormwater pollutant load reduction estimates that support regulatory compliance tracking.

Assessment of spatial representativity of X-ray tomography to study Vertical Flow Treatment wetlands

French Vertical Flow (VF) treatment wetlands receive raw wastewater and provide simultaneous sludge and wastewater treatment. For proper sludge handling, the treatment wetland must be designed adequately and specific operational conditions must be maintained. When these conditions are not met, accumulation of biosolids may lead to clogging. Filtration in French VF Treatment wetlands is governed by mechanisms at the pore-scale. They must be better understood to predict reliably biosolid accumulation. X-ray Computed Tomography (Xray-CT) is a promising technique to characterize in detail the morphology of the filtering media in treatment wetlands. In order to set a solid basis for the use of Xray-CT, the spatial representativity of measurements must be assessed. This issue is addressed in this study by successively analyzing spatial properties at the filter scale using Frequency Domain Electromagnetic Measurements (FDEMs), and at the pore scale using Xray-CT. A map of the electric conductivity at the surface of a French VF Treatment wetland is obtained by FDEM that indicates a homogeneous distribution of biosolids to which electrical conductivity is highly correlated. Different morphological properties were computed from Xray-CT after phase segmentation: phase volume fraction profiles, Specific Surface Area profiles and pore size distributions. Samples show several similarities of pore scale properties obtained by Xray-CT independently of the sampling region and especially the same vertical gradients. FDEM measurements and Xray-CT analysis are in agreement to indicate a good influent distribution at the surface of a full-scale mature French VF Treatment wetland. A criterion to define the limits of the deposit layer and gravel layer is introduced. This division allows to compare layers independently. Finally, a 2D-REV analysis suggests that the selected sample diameter of 5 cm is large enough to be representative of the heterogeneous distribution of phases at the pore-scale as long as no Phragmites are present.

Influence of nanoscale zero-valent iron on hydraulic conductivity of a residual clayey soil and modeling of the filtration parameter

Contaminated clay soils pose problems to public health and the environment in several parts of the world. Very little is known about the transport of decontaminating agents used in remediation process under natural, undisturbed conditions. Nanomaterials, especially those made of nanoscale zero-valent iron (nZVI), have been most frequently used for remediation of contaminated soils because of their higher reactivity, lower toxicity, and lower cost than other metallic nanoparticles. Even though the nanoparticle size is smaller than soil pores, clogging may occur over time due to agglomeration of nanoparticles, which could reduce the soil's natural permeability and thereby cause filtration of the nanoparticles. The use of a stabilizer in the nanoparticles can modify the reactivity but improves their mobility in the soil system. Thus, the objective of this work was to evaluate the hydraulic conductivity of residual clay soil under the injection of different types and concentrations of nZVI with and without surfactant stabilizer (NANOFER 25, NANOFER 25S, and NANOFER STAR in powder at 1 g/L, 4 g/L, 7 g/L, and 10 g/L concentrations), and to model transport of these nZVI suspensions in this soil system. Undisturbed cylindrical soil samples collected from the field were used, and hydraulic conductivity tests were performed using a column apparatus. The results showed that the presence of the stabilizer in the nZVI influenced the nanoparticles' mobility. The nZVI concentrations of 1 and 4 g/L did not affect the natural soil hydraulic conductivity. However, higher concentrations reduced the hydraulic conductivity value, which retarded the migration of nZVI as reflected in the value of filtration parameter.

Bio-carrier and operating temperature effect on ammonia removal from secondary wastewater effluents using moving bed biofilm reactor (MBBR)

This study investigates the impact of bio-carriers' surface area and shape, wastewater chemistry and operating temperature on ammonia removal from real wastewater effluents using Moving bed biofilm reactors (MBBRs) operated with three different AnoxKaldness bio-carriers (K_3, K_5, and M). The study concludes the surface area loading rate, specific surface area, and shape of bio-carrier affect ammonia removal under real conditions. MBBR kinetics and sensitivity for temperature changes were affected by bio-carrier type. High surface area bio-carriers resulted in low ammonia removal and bio-carrier clogging. Significant ammonia removals of 1.420 ± 0.06 and 1.103 ± 0.06 g - N/m². d were achieved by K₃(A_s = 500 m²/m³) at 35 and 20 °C, respectively. Lower removals were obtained by high surface area bio-carrier K₅ (1.123 ± 0.06 and 0.920 ± 0.06 g - N/m². d) and M (0.456 ± 0.05 and 0.295 ± 0.05 g - N/m². d) at 35 and 20 °C, respectively. Theta model successfully represents ammonia removal kinetics with θ values of 1.12, 1.06 and 1.13 for bio-carrier K₃, K₅ and M respectively. MBBR technology is a feasible choice for treatment of real wastewater effluents containing high ammonia concentrations.

Geotextile clogging at different stages of municipal solid waste landfills co-disposed with bottom ash

Co-disposal of bottom ash (BA) with municipal solid waste (MSW) in landfills is a common way for BA management. However, BA co-disposal in MSW landfills may accelerate geotextile clogging and reduce the performance of leachate collection system. This study compared geotextile clogging in a simulated MSW landfill leachate (MSWL) and a BA co-disposed landfill leachate (BAL) at different landfill stages. Geotextile clogging test was conducted using the MSWL and BAL taken from the simulated landfills on the 10th, 80th, 140th and 200th day, respectively. The results demonstrated that geotextile clogging varied with landfill age, due to the change of leachate characteristics. The mass of clogging material in geotextiles with BAL increased from 0.45 g to 2.74 g, which was 43.87%-63.73% greater than those with MSWL. The formation of biofilm was the main contributor for the geotextile clogging. At the same stage, the amount of biofilm formed on geotextile in different leachate was comparable. However, the amounts of CaCO₃ precipitation on geotextile in BAL were 3.85-10.44 times of those in MSW leachate. The pH of leachate played a critical role in CaCO₃ precipitation. The microbial analysis revealed that the co-disposal of the BA greatly influenced the microbial community diversity and structure.

The influence of rainfall intensity and duration on sediment pathways and subsequent clogging in permeable pavements

The trapping of sediments within permeable pavements during infiltration is an important process that contributes to their water quality treatment performance. However, this process also leads to clogging, which decreases the infiltration capacity of the pavement. With different rainfall intensities and durations, this study investigates the amount and size of sediment passing through a porous paver, as well as through the gravel-filled gaps that separate adjacent pavers. One of the major challenges in this study was to design an experiment where the characteristics of the sediment particles that are trapped while passing through these two different infiltration pathways are assessed. This was overcome by developing a new type of rainfall application device in combination with a two-tiered sediment capturing system. A better understanding of the infiltration pathways of sediment and the associated clogging processes should help designers improve the effective life of permeable pavements. Overall, it was found that while the porosity of porous pavers serves a useful function in terms of removing excess surface water during and after a rainfall event, it serves little purpose in removing sediment from stormwater.

Enabling low power acoustics for capillary sonoreactors

Capillary reactors demonstrate outstanding potential for on-demand flow chemistry applications. However, non-uniform distribution of multiphase flows, poor solid handling, and the risk of clogging limit their usability for continuous manufacturing. While ultrasonic irradiation has been traditionally applied to address some of these limitations, their acoustic efficiency, uniformity and scalability to larger reactor systems are often disregarded. In this work, high-speed microscopic imaging reveals how cavitation-free ultrasound can unclog and prevent the blockage of capillary reactors. Modeling techniques are then adapted from traditional acoustic designs and applied to simulate and prototype sonoreactors with wider and more uniform sonication areas. Blade-, block- and cylindrical shape sonotrodes are optimized to accommodate longer capillary lengths in sonoreactors resonating at 28 kHz. Finally, a novel helicoidal capillary sonoreactor is proposed to potentially deal with a high concentration of solid particles in miniaturized flow chemistry. The acoustic designs and first principle rationalization presented here offer a transformative step forward in the scale-up of efficient capillary sonoreactors.

Short-Term Effects on Agricultural Soils Irrigated with Reclaimed Water in Baja California, México

In 2014 reclaimed water (RW) started to be used for agricultural irrigation of 200 ha in Maneadero Valley, Baja California, Mexico. The RW had relatively high electrical conductivity (4-5 dS m^-1), and K⁺, Mg²⁺, PO₄^3- and Cl^- concentrations relative to irrigation guidelines. However, no accumulation of these elements, nor total nitrogen, was observed in the studied soils. The main effect of RW irrigation was the downcore leaching of Cl^- and Na⁺ below 120 cm, causing an increase in electrical conductivity in the lower soil horizons. Al, Fe and Zn showed a twofold to eightfold accumulation in the top soil layer after 2 years. Moderate to severe chemical clogging of dripping systems and potential biological clogging are likely to occur. Mexican national guidelines for the reuse of RW do not take into account specific variables that could change the quality of agricultural soil or lead to clogging of drip irrigation systems.

Evaluation of surface infiltration performance of permeable pavements

Many different test methods are used in practice to evaluate the surface infiltration performance of permeable pavements. This has led to inconsistency in reporting of test results. This study recognizes the differences in nature between a soil infiltration study and the surface infiltration evaluation of permeable pavements, and identifies the main issues associated with the current practice of surface infiltration testing. It proposes that hydraulic conductivity be adopted as the flow property for measurement and reporting instead of the commonly used infiltration rate. The advantages of measuring hydraulic conductivity are elaborated from both theoretical and practical implementation points of view. The theoretical merits of providing a consistent and integrated treatment of surface infiltration performance of a permeable pavement during the design, construction and maintenance phases are presented. The practical benefits are addressed from the following aspects: consistency between laboratory and field testing, uniformity in reporting of test measurements, rationality in construction quality control and acceptance checking, effectiveness in surface infiltration performance monitoring, and enhanced ability in implementing effective maintenance management. It is emphasized that the techniques and methods needed for measuring hydraulic conductivity of permeable pavement materials, for laboratory testing as well as on-site field testing, are already readily available and have been used by researchers and some practitioners for surface infiltration testing. Two falling-head test methods are recommended: one applies Darcy's law and determines hydraulic conductivity in the conventional way; another measures the time history of falling head and calculates hydraulic conductivity using a modified Darcy equation. It is also highlighted that the measurement of hydraulic conductivity offers a convenient platform for assessing the durability of a permeable pavement against clogging.

Direct Analysis of Aqueous Solutions and Untreated Biological Samples Using Nanoelectrospray Ionization Mass Spectrometry with Pipette Tip in Series with High-Ohmic Resistor as Ion Source

Commercially available disposable plastic pipette tip with the inner diameter of ca. 120 μm in series with a high-ohmic resistor (10 GΩ) was adapted as a low-cost alternative ion source for high-throughput nanoelectrospray mass spectrometry (nESI-MS) analysis of a variety of samples, especially aqueous solutions, without sample pretreatment. The use of high-ohmic resistor enabled the formation of stable electrospray of aqueous solutions at ambient conditions. In addition, corona discharge was avoided even with a high voltage applied. Quantitative analysis of vitamin B in water was successfully conducted by tip-ESI. The results exhibited a good linearity (R ˃ 0.9983), a low detection limit (0.25 ng/mL), and a wide dynamic response range (0.25-1000 ng/mL). Our study revealed that tip-ESI not only performed equally well to capillary nESI in terms of flow rate (˂ 100 nL/min), signal sensitivity, and sample consumption, but also offered a number of additional advantages, including better signal duration, tolerance to high analyte concentration (> 100 μg/mL) and high ionizing voltage (up to 6 kV), and obviation of tip clogging and corona discharge. High compatibility of tip-ESI with various kinds of samples (aqueous, viscous, solid, or bulk biological samples) makes it a promising tool for direct MS analysis.

Effects of urban wastewater on hyporheic habitat and invertebrates in Mediterranean streams

Wastewater discharges into fluvial ecosystems represent a significant and continuous source of fine particles and nutrients that can severely modify stream community composition and functionality. Depending on both wastewater and stream features (e.g., nutrient removal treatments and stream dilution capacity), the ecological effects can be more or less severe. To determine how hyporheic habitat and hyporheos are affected, we analysed eight Mediterranean streams both upstream and downstream of a wastewater effluent. The results demonstrated that environmental factors associated with clogging, such as the quantity of fine particulate and organic matter in sediment, were magnified downstream of the wastewater inputs. Likewise, dissolved nutrients also increased but depended to a greater extent on the presence of a wastewater treatment plant and on the nitrogen and phosphorus removal treatments. The hyporheic invertebrates were more affected by clogging than by eutrophication. Both richness and diversity parameters were negatively correlated with clogging features but were not correlated with eutrophication. The most affected taxa were Macrocrustaceans, Hydrachnidia and several insect species, which decreased or were not detected downstream of the effluents. On the contrary, other taxa such as Naididae (Oligochaeta), Orthocladiinae (Chironomidae) and Potamopyrgus antipodarum (Gastropoda) benefited from the wastewater inputs.

fouling in immersed membrane bioreactors

Whilst the fouling of MBR membrane surfaces has been very extensively explored by the academic community, there is an increasingly widespread recognition by practitioners of the issue of clogging of membrane channels with sludge solids, sometimes termed "sludging". The study undertaken has quantified this phenomenon using a bespoke test cell allowing a flat sheet membrane channel to be viewed directly during operation and the accumulated solids determined by digital image processing. Sludging behaviour has then been correlated both with the sludge properties, from sludge samples taken from both an industrial and municipal MBR, and the permeability decline rate data. The work has revealed the expected trends in fouling propensity, as quantified by the exponent n of the Δp/Δt = m.exp(nJ) correlation from classical flux-step tests. With zero membrane aeration the industrial samples exhibited sludging, the filling of the complete thickness of the membrane channel with sludge solids, whereas for municipal sludge the solids formed a cake layer which did not fill the channel. In the absence of sludging the permeability decline followed the expected pattern of increasing at the elevated soluble COD and capillary suction time values of the industrial sludge, compared with municipal sludge at the same solids concentration range (8-12 g.L^-1). However, there was no evident correlation between fouling (permeability decline without sludging) and sludging: incipient sludging did not appear to influence permeability, though can be assumed to negatively impact on long-term operation, or relate to the sCOD concentration. Sludging instead appeared to depend on the sludge physical properties, and primarily the viscosity: sludge samples at high viscosities were found to exhibit a different air-scour pattern to that at normal MLSS concentrations. Outcomes suggest that sludging is caused by rheological conditions promoting bubble coalescence and bubble stream constriction, reducing the exposure of the membrane surface to scouring air.

Acceleration of saturated porous media clogging and silicon dissolution due to low concentrations of Al(III) in the recharge of reclaimed water

The recharge of reclaimed water is an effective strategy for addressing the issues of water quality deterioration and groundwater level decline simultaneously. Residual Al coagulants are normally remained in the recovered water at low concentrations, and may induce clogging problems during the recharging process. However, this issue has been ignored in the past. In this study, we investigated the mechanisms of Al(III)-induced aquifer bio-clogging, the role of Al(III) in quartz sand media (SiO₂) dissolution and re-precipitation in the series of aquifer columns. We determined that Al(III) resulted in serious clogging in ∼140 h at low concentrations that satisfied the national drinking water standard of China. The corresponding hydraulic conductivity decreased by more than ∼90% in the bacteria-containing aquifer, which was ∼30% greater than that for the bacteria-free trials. The enhanced Al(III)-related clogging was caused by modifying quartz sand to form Si-O-Al(OH)n and improving microbes attachment. Microbes retention kinetic coefficients (k) of the Al recharged simulated aquifer could increase by 3.0-8.3 times. The Al(III) also enhanced biomass production and clogging by binding to microbial extracellular polymeric substances. In turn, the greater amount of biomass accelerated the Si dissolution and re-precipitation, this may potentially damage the stability of aquifer structure. The results showed that reclaimed water treated with Al coagulation should be employed with caution for recharging.

Predicting long term removal of heavy metals from porous pavements for stormwater treatment

Porous pavements are commonly used stormwater management systems. However, the understanding of their long-term capacity to retain heavy metals is limited. This study aims to investigate the long-term removal of heavy metals in three different porous pavements - Porous Asphalt (PA), Hydrapave (HP) and Permapave (PP) over accelerated laboratory experiments representing 26 years with varying hydrological conditions (drying/wetting periods and flow rates). A treatment model that simulates adsorption and desorption processes was developed for the first time to predict the long-term heavy metal removal by porous pavements. Unsurprisingly, all tested porous pavements performed better in removing metals that tend to attach to solid particles (e.g. Pb, Al, Fe) than more soluble ones (e.g. Cu, Zn, and Mn). There was a general increase of heavy metal concentrations at the outlet of the pavements over time as a result of a decrease in adsorption capacity of the systems, especially after the occurrence of clogging; the soluble heavy metals removal decreased with a reduction in flow rates which was speculated to be due to more time being available for desorption of metals and breakdown of accumulated sediments. The proposed model simulated the trend, fluctuations and peaks of heavy metal concentrations reasonably well, achieving the Nash-Sutcliffe coefficient (NSE) values of 0.53-0.68 during model calibration. The model was most promising in predicting Al and Cu release from porous pavements (50%-91% of the observed data within the 90% uncertainty bands, NSE = 0.44-0.74), followed by Fe and Pb (27-77% observations within the bands, NSE = 0.20-0.69). Further improvements of the model are needed for it to be applicable for Zn and Mn.

Hydraulic reliability of a horizontal wetland for wastewater treatment in Sicily

The purpose of this study was to evaluate how the hydraulic behavior of a horizontal subsurface wetland (HF), that is part of the hybrid wetland (hybrid-TW) of the IKEA® store in Eastern Sicily (Italy), influences the overall wastewater treatment performance. The HF unit experiences frequent overloading peaks due to the extreme variability in the number of visitors at the store, and after 2 years of operation it showed signals of partial clogging at the inlet area. The hydraulics of the HF unit has been monitored through measurements of hydraulic conductivity at saturation (Ks), tracer tests, and geophysical (i.e. electrical resistivity tomography-ERT) measurements carried out during the years 2016 and 2017. Results indicated a general good agreement between the performed measurement techniques, thus their combination, if adequately performed and calibrated, might be a reliable tool for detecting those wetland areas mainly affected by clogging conditions. The results also indicated that partial clogging had no significant effect on the quality of the discharged water.

Aggregation and clogging phenomena of rigid microparticles in microfluidics: Comparison of a discrete element method (DEM) and CFD-DEM coupling method

We developed a numerical tool to investigate the phenomena of aggregation and clogging of rigid microparticles suspended in a Newtonian fluid transported through a straight microchannel. In a first step, we implement a time-dependent one-way coupling Discrete Element Method (DEM) technique to simulate the movement and effect of adhesion on rigid microparticles in two- and three-dimensional computational domains. The Johnson-Kendall-Roberts (JKR) theory of adhesion is applied to investigate the contact mechanics of particle-particle and particle-wall interactions. Using the one-way coupled solver, the agglomeration, aggregation and deposition behavior of the microparticles is studied by varying the Reynolds number and the particle adhesion. In a second step, we apply a two-way coupling CFD-DEM approach, which solves the equation of motion for each particle, and transfers the force field corresponding to particle-fluid interactions to the CFD toolbox OpenFOAM. Results for the one-way (DEM) and two-way (CFD-DEM) coupling techniques are compared in terms of aggregate size, aggregate percentages, spatial and temporal evaluation of aggregates in 2D and 3D. We conclude that two-way coupling is the more realistic approach, which can accurately capture the particle-fluid dynamics in microfluidic applications.

Characteristics of geotextile clogging in MSW landfills co-disposed with MSWI bottom ash

As a main byproduct of municipal solid waste incineration (MSWI), bottom ash (BA) has become a big challenge in operating MSWI plants. The most common method for BA treatment is co-disposal with MSW in landfills, which may cause clogging in the leachate collection system (LCS). This research investigated the characteristics of geotextile clogging in landfills with BA co-disposal. The co-disposal of BA changed the characteristics of leachate, especially increasing the concentration of Ca²⁺. During the experiment, 0.14 g CaCO₃ was precipitated in the MSW geotextile, while it increased to 0.52 g CaCO₃ in the BA co-disposed geotextile. Based on mass balance of calcium and thermogravimetric (TG) analysis, the formation of biofilm was the main contributor to the mass increment, accounting for about 82% and 57% mass increment in the MSW and BA co-disposed geotextile, respectively. Moreover, CO₂ in landfill gas played an important role in the clogging process, including CaCO₃ precipitation and biofilm formation. The results suggested that the co-disposal of BA with MSW can increase the risk of geotextile clogging in landfills.

Study of the spatial and temporal distribution of accumulated solids in an experimental vertical-flow constructed wetland system

Clogging is the most serious problem in the operation of subsurface flow constructed wetlands (SSF CWs) and is caused by the accumulation of solids in substrates. Study of the solids accumulation process can provide a more accurate reference for the management and maintenance of SSF CWs. In this study, an experimental vertical-flow constructed wetland system was recreated in the lab, and substrates with different depth were sampled through different operation time to reveal the spatial and temporal distribution of accumulated solids. During the study, particulates mainly accumulated through adsorption along the gravel surface. Therefore, the matrix could still provide sufficient space for the particles to pass through and be intercepted or adsorbed into the system at a constant rate. At the end of the study, an increasing number of large particles had been intercepted and were accumulated in the 0-2cm layer of the matrix, indicating a significant decrease in the pore diameter at the top substrate layer. The spatial and temporal accumulation of substrate particulates during the study period was accurately simulated by first-order kinetics models, and the simulated results were in good agreement with measured values.